JP5527204B2 - Fluorine-containing elastic copolymer composition and its crosslinked rubber member - Google Patents

Description

  The present invention relates to a fluorinated elastic copolymer composition capable of providing a crosslinked rubber member excellent in hot water resistance and steam resistance, and a crosslinked rubber member excellent in hot water resistance and steam resistance.

A crosslinked rubber member obtained by crosslinking a fluorinated elastic copolymer is widely used in various applications because it is excellent in heat resistance, weather resistance, chemical resistance, water resistance, insulation and the like.
Among them, the tetrafluoroethylene-propylene copolymer is particularly excellent in base resistance and water resistance, and is used in applications such as alkaline fluid packing, engine oil seal, steam resistance packing, and hot water piping packing. (For example, see Patent Document 1).

  Recently, in food and beverage production facilities, food safety is increasingly important, and it is strongly required to sterilize the production process. Various methods such as sterilization with a chemical solution, sterilization with ozone water, and sterilization with ultraviolet rays are listed as sterilization methods. Also, sterilization with hot water or steam is widely used as an effective sterilization means. Further, the cross-linked rubber member of the fluorinated elastic copolymer has been attracting more and more attention as a material that is durable to all these sterilization means.

In addition, sterilization with hot water or steam is used in food and beverage production facilities, pharmaceutical production facilities, medical facilities, various microorganism test facilities, and the like for culturing microorganisms in order to avoid contamination of microorganisms.
In addition, there are many industrial facilities such as power plants that use hot water or steam as a heat medium, and the hot water resistance and steam resistance of the facilities are increasingly required.
Furthermore, as household equipment, a widespread use of private power generation equipment, hot water supply equipment, and the like, there is a demand for rubber members that have good hot water resistance and steam resistance, and that require less frequent replacement.

  In general, the following methods are known as methods for forming a crosslinked rubber member by molding a fluorinated elastic copolymer. That is, if necessary, a filler, a cross-linking agent, a cross-linking aid, various additives, etc. are added and kneaded using a two-roll, kneader, extruder, etc., and a fluorinated elastic copolymer composition is obtained. Then, the fluorinated elastic copolymer composition is molded by extrusion molding, compression molding using a mold or the like, and simultaneously with or after molding, heating, ionizing radiation irradiation, etc. There is a method of obtaining a crosslinked rubber member by crosslinking using means.

Until now, in the above-mentioned kneading and molding processes, if processing aids such as higher fatty acids, higher fatty acid metal salts, aliphatic amines, natural waxes, polyethylene waxes, etc., are added to the fluorinated elastic copolymer, these operations are carried out. It is known that it becomes easy (see, for example, Patent Document 2 and Non-Patent Document 1). However, it has not been known that these processing aids greatly affect the properties of the crosslinked rubber member obtained from the fluorinated elastic copolymer, particularly hot water resistance and steam resistance.
In particular, in the above application, when the hot water or steam used is 170 ° C. or higher, a crosslinked rubber member of a fluorinated elastic copolymer composition having sufficient hot water resistance and steam resistance is not known. It was.

Japanese Patent Laid-Open No. 53-9848 Japanese Patent Laid-Open No. 7-196879 New edition of rubber technology basics (edited by the Japan Rubber Association) Second edition (issued on November 30, 2005) 166 pages

  An object of the present invention is to provide a fluorinated elastic copolymer composition capable of providing a crosslinked rubber member excellent in hot water resistance and steam resistance, and a crosslinked rubber member excellent in hot water resistance and steam resistance obtained by crosslinking the same. Is to provide.

The present invention provides a fluorinated elastic copolymer composition and a crosslinked rubber member having the following constitutions.
[1] The compound represented by the general formula (1) is 0.1% with respect to 100 parts by mass of the fluorinated elastic copolymer and the compound represented by the following general formula (1). A fluorine-containing elastic copolymer containing 10 to 10 parts by mass, further containing an organic peroxide, and containing triallyl cyanurate, triallyl isocyanurate, or trimethallyl isocyanurate Compositions (except those containing barium stearate) .
(RCOO ⁻ ) _n M ^{n +} (1)
(In the formula, R is an organic group having 10 to 30 carbon atoms, n is an integer of 2 or 3, M is an alkaline earth metal, Zn, Cd, Co, Sn, Cu, Pb, Ni or Al. .)

[2] The fluorinated elastic copolymer composition according to the above [1], wherein R in the general formula (1) is a saturated linear aliphatic hydrocarbon group having 10 to 25 carbon atoms.
[3] The fluorinated elastic copolymer composition according to the above [1] or [2], wherein M in the general formula (1) is Mg, Ba, Ca, Zn, or Al.
[4] The compound represented by the general formula (1) is zinc stearate, calcium stearate, at least one member selected from the group consisting of magnesium stearate and aluminum stearate, the above-mentioned [1] to [3] The fluorinated elastic copolymer composition according to any one of the above.
[5] The fluorinated elastic copolymer composition according to any one of [1] to [4] above, an organic peroxide, triallyl cyanurate, triallyl isocyanurate, or trimethallyl isocyanurate, Alternatively, a crosslinked rubber member obtained by crosslinking with ionizing radiation.

[ 6 ] The fluorinated elastic copolymer composition according to the above [ 5 ], which has a volume swelling ratio of 10% or less in a hot water test at 180 ° C. for 70 hours in accordance with JIS K6258.
[ 7 ] The fluorinated elastic copolymer composition according to the above [ 5 ], wherein the volume swelling ratio in a steam resistance test at 170 ° C. for 70 hours in accordance with JIS K6258 is 10% or less.
[ 8 ] A member for a heat-resistant water device, comprising the crosslinked rubber member according to any one of [ 5 ] to [ 7 ].
[ 9 ] A component member for a steam resistant device, comprising the crosslinked rubber member according to any one of [ 5 ] to [ 7 ].

  The fluorinated elastic copolymer composition of the present invention can provide a crosslinked rubber member having excellent hot water resistance and steam resistance even under severe conditions. The crosslinked rubber member of the present invention is excellent in hot water resistance and steam resistance, as well as in heat resistance, weather resistance, chemical resistance, insulation, and mechanical properties.

  The cross-linked rubber member of the present invention is used as a structural member such as a sealing material used when sterilizing food, beverage and other manufacturing equipment, pharmaceutical manufacturing equipment, medical equipment, various microorganism testing equipment, etc. with hot water or steam. It can be used suitably. Moreover, it can be suitably used as a structural member such as a sealing material for industrial equipment, such as a power plant, which uses hot water or steam as a heat medium, household equipment such as private power generation equipment, hot water supply equipment, etc. . Furthermore, the crosslinked rubber member of the present invention is excellent in durability in all these sterilizing means. In particular, when the hot water or steam used is 150 ° C. or higher, more significantly 170 ° C. or higher, the crosslinked rubber member of the present invention is extremely effective as a sealing material.

The fluorinated elastic copolymer in the present invention is a copolymer containing repeating units based on a fluorinated monomer.
Examples of the fluorine-containing monomer include fluoroolefins such as tetrafluoroethylene, vinylidene fluoride, hexafluoropropylene, chlorotrifluoroethylene, and vinyl fluoride; perfluoro such as perfluoro (methyl vinyl ether) and perfluoro (propyl vinyl ether). (Alkyl vinyl ethers); (perfluoroalkyl) ethylenes such as trifluoromethylethylene and pentafluoroethylethylene;

  The fluorinated elastic copolymer of the present invention can contain a repeating unit based on a hydrocarbon-based monomer not containing fluorine. Examples of the hydrocarbon-based monomer not containing fluorine include olefins such as ethylene, propylene, butene and isobutene; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl esters such as vinyl acetate;

  Specific examples of the fluorinated elastic copolymer include tetrafluoroethylene-propylene copolymer, tetrafluoroethylene-propylene-vinylidene fluoride copolymer, tetrafluoroethylene-propylene-perfluoroalkylethylene copolymer, ethylene -Tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoro (alkyl vinyl ether) ) Copolymer, vinylidene fluoride-perfluoro (alkyl vinyl ether) -tetrafluoroethylene copolymer, tetrafluoroethylene-perfluoro (alkyl vinyl ether) copolymer, etc. It is.

  Of these, a tetrafluoroethylene-propylene copolymer is preferable from the viewpoint of hot water resistance and steam resistance. The molar ratio of the repeating units based on tetrafluoroethylene / the repeating units based on propylene in the tetrafluoroethylene-propylene copolymer is preferably 90/10 to 10/90, more preferably 70/30 to 30/70, and 70 / 30-50 / 50 is most preferred.

The fluorinated elastic copolymer in the present invention may contain repeating units based on monomers having various crosslinkable functional groups. When a repeating unit based on a monomer having a crosslinkable functional group is contained, the crosslinking reactivity can be increased by heat-treating the fluorinated elastic copolymer.
As monomers having a crosslinkable functional group, monomers containing iodine atom or bromine atom; vinyl esters such as vinyl acrylate, vinyl methacrylate, vinyl crotonate, vinyl chloroacetate, vinyl bromoacetate; vinyl glycidyl ether, allyl And vinyl ethers such as glycidyl ether, hydroxyethyl vinyl ether, hydroxybutyl butyl vinyl ether, and chloroethyl vinyl ether.

The content of the repeating unit based on the monomer having a crosslinkable functional group is preferably from 0.1 to 20 mol%, more preferably from 0.1 to 10 mol% in the fluorinated elastic copolymer. The fluorinated elastic copolymer may be a polymer having an iodine atom terminal or a bromine atom terminal.
The Mooney viscosity ML _{1 + 4} (100 ° C.) of the fluorinated elastic copolymer used in the present invention is not particularly limited, but is preferably 20 to 180, and more preferably 30 to 150. Mooney viscosity is a measure of various average molecular weights. A high Mooney viscosity indicates a high molecular weight, and a low Mooney viscosity indicates a low molecular weight. A Mooney viscosity within the above range is preferable because of excellent moldability.

The fluorinated elastic copolymer composition of the present invention contains a compound represented by the following general formula (1).
(RCOO ⁻ ) _n M ^{n +} (1)
(In the formula, R is an organic group having 10 to 30 carbon atoms, n is an integer of 2 or 3, M is an alkaline earth metal, Zn, Cd, Co, Sn, Cu, Pb, Ni or Al. .)
R in the compound represented by the general formula (1) is an organic group having 10 to 30 carbon atoms. 10-25 are preferable, as for carbon number of an organic group, 10-20 are more preferable, and 12-18 are the most preferable.

The organic group in the general formula (1) may be saturated or unsaturated, is preferably an aliphatic hydrocarbon group, more preferably a linear aliphatic hydrocarbon group, and most preferably a saturated linear aliphatic hydrocarbon group. The compound represented by the general formula (1) is a compound generally known as a metal salt of a higher fatty acid.
The compound represented by the general formula (1) may be a naturally derived component such as animal fatty acid or an artificially synthesized component. Moreover, the mixture of a 2 or more types of carbon number fatty acid may be sufficient.

M in the general formula (1) is an alkaline earth metal, Zn, Cd, Co, Sn, Cu, Pb, Ni, or Al, but is preferably an alkaline earth metal, Zn, Pb, Al, Mg, Ba, Ca, Zn and Al are more preferable, Ca and Al are further preferable, and Ca is most preferable.
Specific examples of the compound represented by the general formula (1), calcium stearate, zinc stearate, magnesium stearate, aluminum stearate, cadmium stearate, cobalt stearate, tin stearate, lead stearate, copper stearate , Nickel stearate, lithium stearate, calcium ricinoleate, zinc palmitate, aluminum myristate and the like. These 1 type (s) or 2 or more types are mix | blended with a fluorinated elastic copolymer.

Compound represented by the general formula (1), inter alia, calcium stearate, zinc stearate, magnesium stearate, aluminum stearate are preferred, calcium stearate, aluminum stearate are more preferred. Furthermore, calcium stearate is most preferred.
Content of the compound represented by General formula (1) is 0.1-10 mass parts with respect to 100 mass parts of a fluorine-containing elastic copolymer. The content is appropriately determined within the above range depending on the composition of the fluorinated elastic copolymer composition containing a filler or additive suitable for obtaining the desired crosslinked rubber member. The content is preferably 0.2 to 5 parts by mass, more preferably 0.2 to 3 parts by mass, and most preferably 0.3 to 2 parts by mass. If the content is too small, the moldability is inferior, and if it is too large, the heat resistance of the resulting crosslinked rubber member may be lowered. Within the above range, the moldability is excellent and the cross-linked rubber member is remarkably excellent in hot water resistance and steam resistance.

Fluorinated elastic copolymer composition of the present invention may be cross-linked, it gives a crosslinked rubber member. By crosslinking by crosslinking or ionizing radiation by the organic peroxide, crosslinking rubber member having excellent hot water resistance and steam resistance are obtained. In these cross-linking methods, the cross-linked rubber member is considered to be excellent in hot water resistance and steam resistance because the chemical bond by cross-linking is a covalent bond with no ionization separation or small charge separation.

  As the organic peroxide used for crosslinking, an organic peroxide is usually used. Specific examples of the organic peroxide include benzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane, 2,5 -Dimethyl-2,5-bis (t-butylperoxy) hexyne-3, α, α'-bis (tert-butylperoxy) -p-diisopropylbenzene, 1,1-bis (tert-butylperoxy) -3,3,5-trimethylcyclohexane and the like.

  The content of the organic peroxide is preferably 0.3 to 10 parts by mass with respect to 100 parts by mass of the fluorinated elastic copolymer. When the content is less than 0.3 parts by mass, crosslinking may be insufficient. When the amount is more than 10 parts by mass, the elasticity of the crosslinked rubber member may be lost. More preferably, the content of the organic peroxide is 0.5 to 3 parts by mass.

In cross-linking with ionizing radiation, a cross-linking agent may be blended in the fluorinated elastic copolymer composition. Moreover, it is not necessary to mix | blend a crosslinking adjuvant. Examples of radiation to be irradiated include electron beams, gamma rays, and ultraviolet rays. The irradiation amount in electron beam irradiation is preferably 1 to 2000 kGy, and more preferably 10 to 200 kGy.
Examples of the crosslinking agent used for crosslinking by ionizing radiation include dicumyl peroxide, 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane, and α-α'-bis (tert-butylperoxy). ) -P-diisopropylbenzene and the like, and dicumyl peroxide and α-α'-bis (tert-butylperoxy) -p-diisopropylbenzene are preferable.
The content of the crosslinking agent is preferably 0.3 to 10 parts by mass, more preferably 0.5 to 3 parts by mass with respect to 100 parts by mass of the fluorinated elastic copolymer.

The crosslinking by crosslinking or ionizing radiation by the organic peroxide, a fluorinated elastic copolymer composition is formulated the following unsaturated functional compound as a crosslinking agent.
The crosslinking aid is triallyl cyanurate, triallyl isocyanurate, or trimethallyl isocyanurate , more preferably triallyl isocyanurate.

The content of the crosslinking aid is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and most preferably 1 to 5 parts by mass with respect to 100 parts by mass of the fluorinated elastic copolymer. .
In the fluorinated elastic copolymer composition of the present invention, various compounds conventionally used in the production of crosslinked rubber members can be further blended as necessary.
Specific examples of the compounding agent include fillers such as carbon black, silica, clay, talc and glass fiber, pigments such as titanium oxide and bengara, resins and rubbers other than the fluorinated elastic copolymer.

The fluorinated elastic copolymer composition of the present invention is easily produced by uniformly mixing each of the above components with a rubber mixing device such as a roll, a kneader, a Banbury mixer, or an extruder.
The fluorinated elastic copolymer composition of the present invention can be molded by an ordinary rubber molding method. Examples of the molding method include compression molding, injection molding, extrusion molding, calendar molding, dipping in a solvent, coating, and the like.

The fluorinated elastic copolymer composition of the present invention can be crosslinked simultaneously with molding or after molding to obtain a crosslinked rubber member.
For crosslinking with an organic peroxide, hot press crosslinking, steam crosslinking, hot air crosslinking, lead-based crosslinking, or the like is employed in consideration of the molding method and the shape of the crosslinked rubber member. The crosslinking condition is usually preferably 100 to 400 ° C. for several seconds to 24 hours, more preferably 140 to 250 ° C. for 1 minute to 1 hour. Further, secondary crosslinking is preferably employed for the purpose of improving mechanical properties, compression set and other properties of the crosslinked rubber member. The conditions for secondary crosslinking are preferably 100 to 300 ° C. for 30 minutes to 48 hours, more preferably 140 to 250 ° C. for 1 to 24 hours.
Moreover, there is no restriction | limiting of the temperature at the time of bridge | crosslinking in bridge | crosslinking by ionizing radiation. If necessary, the crosslinked rubber member obtained by crosslinking with an organic peroxide can be further irradiated with ionizing radiation to increase the crosslinking density.

The crosslinked rubber member of the present invention has a volume expansion coefficient in a hot water resistance test at 180 ° C. of 70 hours in accordance with JIS K6258 and a steam resistance test in 170 ° C. of 70 hours in accordance with JIS K6258. It is preferably within 10%, more preferably within 8%, even more preferably within 5%, and most preferably within 3%.
The crosslinked rubber member of the present invention is useful for O-rings, seals, packings, gaskets, valves, tubes, hoses, rolls, sheets, connectors, and the like of food production facilities that perform steam sterilization, hot water sterilization, and the like.
In addition, the cross-sectional shape of the ring, seal | sticker, and packing produced using the bridge | crosslinking rubber member of this invention may be a thing of various shapes. Specifically, for example, the shape may be a square, an O-shape, a ferrule, or a different shape such as a D-shape, an L-shape, a T-shape, a V-shape, an X-shape, or a Y-shape.

Next, the present invention will be described more specifically with reference to examples. In addition, this invention is not restrict | limited at all by these examples, and is not interpreted.
The hot water resistance test and the steam resistance test of Examples and Comparative Examples were performed by the following methods.
In Tables 1 to 4, the amount of each component used is shown in parts by mass.
[Heat resistance test]
The measurement was performed according to JIS K6258. In the hot water resistance test of the crosslinked rubber member, the crosslinked rubber member was placed in a sealed container together with a predetermined amount of water sufficient to immerse, heated at 180 ° C. for 70 hours, and then cooled to room temperature. Thereafter, the change in physical properties of the crosslinked rubber member was measured within 30 minutes after taking out the crosslinked rubber member from the sealed container.

[Steam resistance test]
The measurement was performed according to JIS K6258. In the steam resistance test of the crosslinked rubber member, the crosslinked rubber member is placed in a sealed steam generator together with a predetermined amount of water sufficient to generate steam, placed in a steam environment at 170 ° C. for 70 hours, and then to room temperature. Cooled down. Subsequently, the change in physical properties of the crosslinked rubber member was measured within 30 minutes after taking out the crosslinked rubber member from the sealed container.

[Examples 1 to 3 ]
According to the components and blending amounts shown in Table 1, fluorinated elastic copolymer composition 1 and fluorinated elastic copolymer-2 were mixed uniformly with two rolls to obtain a fluorinated elastic copolymer composition. Manufactured.
The obtained fluorinated elastic copolymer composition was press-crosslinked at 170 ° C. for 20 minutes. Thereafter, secondary crosslinking was performed in an oven at 180 ° C. for 4 hours to obtain a crosslinked rubber member.
Using the obtained crosslinked rubber member, normal properties were measured, and a hot water resistance test was conducted. The results are shown in Table 1.

[Comparative Examples 1-3]
According to the components and blending amounts shown in Table 2, a fluorinated elastic copolymer composition was produced and crosslinked in the same manner as in Example 1 to obtain a crosslinked rubber member. Using the obtained crosslinked rubber member, normal properties were measured, and a hot water resistance test was conducted. The results are shown in Table 2.

[Examples 5 to 7 ]
According to the components and blending amounts shown in Table 3, the fluorinated elastic copolymer-1 was produced by uniformly mixing the fluorinated elastic copolymer-1 with two components using two rolls.
The obtained fluorinated elastic copolymer composition was press-crosslinked at 170 ° C. for 20 minutes. Subsequently, secondary crosslinking was performed in an oven at 180 ° C. for 4 hours to obtain a crosslinked rubber member.
Using the obtained crosslinked rubber member, normal properties were measured and a steam resistance test was performed. The results are shown in Table 3.

[Comparative Examples 4 to 5]
According to the components and blending amounts shown in Table 4, a fluorinated elastic copolymer composition was produced and crosslinked in the same manner as in Example 6 to obtain a crosslinked rubber member. Using the obtained crosslinked rubber member, normal properties were measured and a steam resistance test was performed. The results are shown in Table 4.

In addition, the symbol shown in Tables 1-4 is as follows.
Fluorine-containing elastic copolymer-1: Aflas 150P (Asahi Glass Co., Ltd., tetrafluoroethylene-propylene copolymer, Mooney viscosity ML _{1 + 4} (100 ° C.) 95).
Fluorine-containing elastic copolymer-2: Daiel G-902 (manufactured by Daikin Industries, Ltd., vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, Mooney viscosity ML _{1 + 4} (100 ° C.) 50).
TAIC: triallyl isocyanurate (manufactured by Nippon Kasei Co., Ltd.)
Parkadox 14: α, α′-bis (tert-butylperoxy) -p-diisopropylbenzene (manufactured by Kayaku Akzo).
Perhexa 25B: 2,5-dimethyl-2,5-bis (tert-butylperoxy) hexane (manufactured by NOF Corporation).

[Example 8 ]
A packing is produced using the fluorinated elastic copolymer composition having the composition shown in Example 1. When used as a packing in a food production process, it exhibits good durability against steam (170 ° C.) used during sterilization of the process.

The crosslinked rubber member obtained from the fluorinated elastic copolymer composition of the present invention is an O-ring, seal, packing, gasket, valve, tube, hose, roll, sheet of food production equipment that performs steam sterilization, hot water sterilization, etc. Useful for connectors, etc. In addition, microbial culture members that sterilize using steam and hot water, industrial and household equipment members that require steam and hot water piping, hot water and steam are used as the heat medium It is useful for components such as power generation equipment members and sealing materials exposed to hot water and steam.

The entire contents of the specification, claims, and abstract of Japanese Patent Application No. 2008-131972 filed on May 20, 2008 are incorporated herein as the disclosure of the specification of the present invention. Is.

Claims (9)

The compound represented by the general formula (1) is 0.1 to 10 masses per 100 parts by mass of the fluorinated elastic copolymer and the compound represented by the following general formula (1). A fluorine-containing elastic copolymer composition comprising an organic peroxide, triallyl cyanurate, triallyl isocyanurate, or trimethallyl isocyanurate ( (Excluding those containing barium stearate) .
(RCOO ⁻ ) _n M ^{n +} (1)
(In the formula, R is an organic group having 10 to 30 carbon atoms, n is an integer of 2 or 3, M is an alkaline earth metal, Zn, Cd, Co, Sn, Cu, Pb, Ni or Al. .)   2. The fluorinated elastic copolymer composition according to claim 1, wherein R in the general formula (1) is a saturated linear aliphatic hydrocarbon group having 10 to 25 carbon atoms.   The fluorine-containing elastic copolymer composition according to claim 1 or 2, wherein M in the general formula (1) is Mg, Ba, Ca, Zn, or Al. Compound represented by the general formula (1) is free, wherein zinc stearate, calcium stearate, to any one of claims 1 to 3 is at least one selected from the group consisting of magnesium stearate and aluminum stearate Fluoroelastic copolymer composition.   The fluorinated elastic copolymer composition according to any one of claims 1 to 4 is crosslinked with an organic peroxide and triallyl cyanurate, triallyl isocyanurate, trimethallyl isocyanurate, or ionizing radiation. A cross-linked rubber member characterized by being made to be.   The crosslinked rubber member according to claim 5, wherein the crosslinked rubber member has a volume swelling ratio of 10% or less in a hot water test at 180 ° C for 70 hours in accordance with JIS K6258.   The cross-linked rubber member according to claim 5, wherein the cross-linked rubber member has a volume swelling ratio of 10% or less in a steam resistance test at 170 ° C for 70 hours in accordance with JIS K6258.   A constituent member for a heat-resistant water device comprising the crosslinked rubber member according to any one of claims 5 to 7.   A constituent member for a steam resistant device, comprising the crosslinked rubber member according to any one of claims 5 to 7.